1. Field of the Invention
The invention relates to a novel photosensitive colored composition and a color filter. A photosensitive colored composition according to the invention is suitably used for image-forming materials such as optical color filters and solder resists. In particular, the present invention relates to a photosensitive colored composition that is suitably used for preparing color filters for use in color liquid crystal displays, color image tube devices and the like, and to a color filter using the same.
2. Description of the Related Art
Color filters for use in, e.g., color liquid crystal displays, and color image tube devices are produced by forming two or more colored images different in color tone in the fine stripe, mosaic, or other pattern on a transparent substrate such as a glass substrate. The pattern width varies according to the applications of the color filter, but is usually approximately 5 to 700 μm. In addition, the accuracy of position in superimposing the patterns is several to dozens μm, and thus color filters are produced by using microfabrication technology superior in dimensional accuracy.
Methods of producing color filters include dyeing, electrodeposition, printing, and pigment dispersion, but considering the productivity, quality, cost, and others together, the pigment dispersion method is most favorable and thus has been used widely as the method of producing color filters. The pigment dispersion method is a method of producing a color filter by forming a colored image on a substrate with a color resist formed of a colored photosensitive resin composition containing an organic pigment dispersed therein by photolithography.
However, in the pigment dispersion method, it has been difficult to stably disperse pigments and in particular to select a suitable dispersing resin, which has a significant influence on the dispersion stability of pigments.
The color resist is generally applied onto a glass substrate by using a spin coater, but if the fluidity of the pigment is insufficient, it is difficult to obtain a uniform coated film.
The viscosity of color resists, or pigment dispersions, is known to depend generally on shear rate. Because the thickness of the color resist film obtained by spin coating is proportional to the viscosity of the color resist, the viscosity of the color resist when applied should be kept the same in the central and outer surface areas of the transparent substrate for production of a uniform coated film.
When a color resist is dispensed and rotated on a substrate, the apparent viscosity of the color resist in the central area is close to the viscosity when the shear rate is lower, because the color resist has a lower linear centrifugal velocity there. On the contrary, the apparent viscosity of the color resist in the outer peripheral area on the substrate is close to the viscosity when the shear rate is higher, because the color resist has a higher linear velocity there. As a result, the color resist, which is thixotropic in nature, provides a film greater in thickness in the central area on the substrate where the shear rate is lower and the apparent viscosity is higher, and thinner in thickness in the outer peripheral area on the substrate where the shear rate is higher and the apparent viscosity is lower. Because a color filter should have a uniform film thickness all over the substrate, a color resist for production of the color filter should be a fluid having a uniform viscosity independent of the shear rate, i.e., a Newtonian fluid.
As color filters demand a particularly high transparency, dispersions containing very fine pigment particles dispersed uniformly in transparent vehicles have been used.
It is known to be difficult to obtain a stabilized dispersion by dispersing fine pigment particles in vehicles, causing various problems in production and of the quality of the resulting products. For example, a dispersion containing fine pigment particles often shows a high viscosity, making it difficult to discharge the product dispersion from a dispersing machine and to transport the product and, to make matters worse, making itself unusable due to gelation during storage. It may also cause the troubles of deterioration in transparency of the color resist-coated film, leveling defects, and the like. Accordingly, there exists a need for a method of dispersing a finer pigment in a more stabilized manner, for production of color filters superior in transparency by the pigment dispersion method.
In addition, pigment particles in a color resist often coagulate gradually over time, raising the viscosity and enhancing the thixotropic property of the dispersion. Thus, when the color resists are coated by a spin coater, color resists immediately after production and after storage for a certain period of time provide coated films different in thickness and uniformity.
For these reasons, it is quite important that the color resist is a Newtonian fluid and retains its physical properties unchanged for an extended period of time.
Color resists are sometimes coated by a coater other than the spin coater, such as a slit & spin coater, a roll coater, or a curtain coater. The color resists are supplied to nozzles, slit dies, and the like from their chemicals tanks via piping made of, for example, polytetrafluoroethylene, polypropylene, or the like and air-operated valves.
When a conventional photosensitive colored composition is coated by the coater noted above, insoluble aggregates accumulate in the piping made of, for example, polytetrafluoroethylene, polypropylene, or the like, inside of air-operated valves, dispense nozzles, the tips of slit dies, and the like because of its low dispersion stability of pigment, resulting in the foreign-matter defects of the color filter caused by the aggregates and thus drastic decrease in productivity.
To overcome the various problems above, methods of using a pigment derivative having an organic pigment as a skeleton and an acidic or basic substituent group as a dispersant have been proposed (see, for example, Jpn. Pat. Appln. KOKOKU Publication No. 41-2466, U.S. Pat. No. 2,855,403, and Jpn. Pat. Appln. KOKAI Publication Nos. 63-305173, 1-247468, and 3-26767).
In addition, use of a copolymer having an alkyleneoxy group has been also proposed (see, for example, Jpn. Pat. Appln. KOKOKU Publication No. 62-25164, and Jpn. Pat. Appln. KOKAI Publication Nos. 4-223468 and 5-39450).
However, it is still difficult to obtain satisfactory effects even by use of these methods, although there are some exceptions.